In this experiment, we adopted the 4-qubit Hamiltonian \(H_{hydrogen}\)  for the hydrogen molecule \(\text{H}_2\)  generated by the Pennylane-QChem [1]} package, when the coordinates of the two hydrogen atoms are \((0, 0, -0.66140414)\)  and \((0, 0, 0.66140414)\) , respectively, in atom units. The goal of this experiment is to find an ansätz that can produce similar states as the four-qubit Givens rotation for single and double excitation.
The unitary operator see https://pennylane.readthedocs.io/en/latest/code/api/pennylane.SingleExcitation.html that performs single excitation on a subspace spanned by \(\lbrace {01}, {10} \rbrace \)  can be written as
\(U(\phi )=\left[\begin{array}{cccc}1 & 0 & 0 & 0 \\0 & \cos (\phi / 2) & -\sin (\phi / 2) & 0 \\0 & \sin (\phi / 2) & \cos (\phi / 2) & 0 \\0 & 0 & 0 & 1\end{array}\right]\) 
